The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
A continuously variable transmission (“CVT”) typically includes a belt and pulley system that operatively couples a rotary power source, such as an engine or electric motor, to a double gear final drive unit. The belt and pulley system generally includes first and second pairs of pulley cones having a torque transmitting belt or chain extending between the cone pairs. Each pulley cone pair includes an axially stationary pulley member and an axially movable pulley member. Each movable pulley member is axially adjustable with respect to the stationary pulley member by a hydraulic system. The hydraulic system provides primary and secondary hydraulic pressures to the respective movable pulley members to adjust the running radius of the first and second pulley cone pairs which in turn controls the output/input ratio of the continuously variable transmission. Movement of the cones steplessly or continuously varies the ratio of an input speed to an output speed. With the continuously variable transmission, small but effective ratio changes can be attained. This is in contrast to a fixed gear ratio unit where any ratio changes are step values.
In many CVT's, engine torque is transferred from the pulley to the belt via friction by clamping the belt between the pulleys. The required clamping force, therefore, is a function of the amount of torque being transferred through the belt where higher levels of engine torque require higher levels of clamping force on the belt to prevent slippage. Yet generally speaking, the higher the clamping force required, the more wear on the belt and the less efficient the system. Accordingly, there is a need for improved CVT designs that reduces the required clamping forces on the belt to improve the efficiency of the CVT.